Initiator systems



1967 D. J. DITTMANN ETAL 3,358,601

INITIATOR SYSTEMS Filed June 29, 1966 FIG. 3

INVENTORS FIG; 2

DAVID J. DITTMANN HIRAM E. DRISCOLL DONALD P. GRAHAM AGENT United States Patent M 3,358,601 INITIATOR SYSTEMS David J. Dittmann and Hiram E. Driscoll, Woodstock,

and Donald P. Graham, Hurley, N.Y., assignors to Hercules Incorporated, Wilmington, DeL, a corporation of Delaware Filed June 29, 1966, Ser. No. 561,550 10 Claims. (Cl. 10228) ABSTRACT OF THE DISCLOSURE Self-desensitizing primary and secondary initiator systems of the blasting cap, and booster, type are provided, which are formed from an elongated shell containing a passageway in the bottom end thereof, of size correlated with at least one of the live initiator components to convey ingress of water into the shell to cause desensitization of the live component(s) after a predetermined period of time following emplacement of the system in a water-covered area; and, in certain embodiments a waterresistant member, within the shell, is superposed on the passageway as a closure therefor to regulate water ingress.

This invention relates to primary and secondary initiator systems for initiating explosives in water-covered areas, and which are particularly advantageously applied to offshore seismic exploration. In one aspect this invention relates to such systems which are capable of normal function for a predetermined period after emplacement in a Water-covered blasting environment, but adapted to become desensitized after that time, being thereby capable of normal function under conventional firing conditions but free from potential hazards that develop following misfires.

Complete explosive assemblies constitute a combina tion of main charge, with means for initiating same. For example, one such assembly constitutes an explosive carfridge containing a main explosive charge such as a nitrocarbonitrate, a secondary initiator containing a booster charge, and a primary initiator containing an ignition composition and at least one charge detonatable in response to ignition of the ignition composition together with means for ignition of the ignition composition. The booster charge is detonated in response to ignition of the ignition composition and subsequent detonation of the detonatable charge associated therewith, and the main charge is detonated in response to detonation of the booster charge to provide the full explosive force of the main charge of the assembly.

A typical and generally utilized primary initiator is an electric blasting cap of either the instantaneous or delay type, containing a base charge, a primer charge, an ignition composition, and means for ignition of the ignition composition. The primer charge is detonatable in response to ignition of the ignition composition, and the base charge is detonatable in response to detonation of the primer charge. In some instances, the primer and ignition compositions are one and the same, but in all events the base charge is in operative communication with the ignition composition to detonate in response to ignition of same. In a delay-type electric blasting cap, as a primary initiator, a fuse is disposed intermediate the ignition composition and the primer charge to provide delay in detonation of the primer after ignition.

A typical and generally utilized secondary initiator is a booster cartridge containing a high explosive, as a booster charge, and a well for supporting a primary initiator in operative communication with the booster charge so as to initiate detonation of same. The secondary ini- 3,358,651 Patented Dec. 19, 1967 tiator is generally supported in a well in the main charge of the assembly for detonation of the main charge.

In the emplacement of a complete explosive assembly in a water-covered area, it is often necessary that there be long lines of communication between the primary initiator of the assembly and the power source. There are also various support lines utilized in the handling of the assembly during its emplacement in the shooting area. It can be readily appreciated, therefore, that in the emplacement and firing of the assembly there will 'be from time to time failures of the system or damage imparted to the lead and communication lines, generally with loss of the assembly, the result in all events being a misfiring, i.e. failure to shoot due to loss of communication with the energy source. In many such instances of misfiring the assembly remains live, uncontrolled, and retrievable with great difliculty, if retrievable at all.

Misfiring of assemblies in water-covered areas, and especially in areas of offshore seismic exploration, presents serious safety hazards in respect to property and persons in the adjacent shoreline area. In many such intances, complete assemblies, or components separated therefrom, still live but out of control, are eventually washed ashore and are subject to accidental firings to impair the safety of the adjacent shore areas and of persons frequenting such areas who are unskilled in the art of explosives and who can be seriously injured in encountering the live elements, such as when endeavoring to handle them.

Oifshore seismic exploration, in view of the misfirings that often occur at the shooting site, with concomitant washing ashore of the still live elements of the seismic explosive assembly that remain, has presented such hazards to shore areas that in some instances local government authorities have deemed it necessary to halt the exploration work taking place off their shores until there can be assurance that explosive assemblies or components thereof resulting from misfirings will not impair the safety of their shore areas.

This invention is concerned with primary and secondary initiator systems, i.e. of the blasting cap and booster types, adapted to function normally in a complete explosive assembly, in water-covered blasting areas, for a predetermined period and to become desensitized after that time, to thereby be free from potential hazards of uncontrolled shots following misfirings. The invention is particularly concerned with such initiators utilized in olfshore seismic exploration assemblies.

In accordance with the invention, an initiator system of the blasting cap and booster type, for initiating explosives in water-covered areas, is provided, which comprises an elongated closed shell, and a base explosive charge within said shell, as at least one live initiator component of said system, extending from the closure at one end of said shell toward the opposite end thereof; said shell containing a passageway in the said closure end thereof containing said base charge to communicate said base charge with the outside of said shell; and the size of said passageway being correlated with at least one live component within said shell to convey flow of water from outside said shell to the shell interior to cause desensitization of the last said component after a predetermined period of time following emplacement of said system in said water-covered area.

The invention is illustrated with reference to the drawings of which FIGS. 1 and 2 are cross-sectional views illustrative of electric blasting cap type primary initiators of the invention; FIGS. 3 and 4 are cross-sectional views illustrative of booster-type secondary initiators of the invention; and FIG. 5 is a cross-sectional view illustrative of a now-preferred complete explosive assembly contain- 3 ing a primary initiator component of FIG. 1 and a secondary initiator component of FIG. 4.

Referring to FIG. 1, primary initiator system of the electric blasting cap type, which comprises, an elon.

gated shell 9, a high explosive 11 such as PETN (pentaerythritol tetranitrate), as base charge, disposed adjacent the closed bottom end 12 extending toward the interior of the shell; primer charge 13, such as diazodinitrophenol, superposed on base charge 11; ignition composition 14, such as a lead-selenium ignition mixture, superposed on primer 13; dielectric wire support plug 16, such as Bakelite closing shell 9 superposed on ignition composition 14; and'a top closure plug 17, for shell 9, such as a resin wax composition superposed on plug 16. Insulated electric conductor wires 18 (insulation 21) extend through top end 19 of shell 9, at least into closure 17, and continue without insulation into ignition mixture 14, connecting therein, at their terminal ends, with bridge wire 22.

Base charge 11 is any suitable high explosive normally utilized as such in electric blasting caps as, for example, PET N, tetryl, RDX, and the like, and is generally characterized by a detonation rate above about 7,000 m./sec., usually not exceeding about 10,000 m./sec. Primer charge 13 is any suitable charge normally utilized as such in electric blasting caps, such as diazodinitrophenol, nitromannite, and the like. Ignition composition 14 is any suitable ignition composition normally utilized as such in electric blasting caps such as Pb/Se, lead mononitroresorcinate, lead oxide/boron, red lead/ manganese boride, and the like, whether loose or compressed, or of matchhead design.

Base charge 11 is detonatable in response to detonation of primer 13, and is disposed in operative communication with primer charge 13 to so detonate; primer charge 13 is detonatable in response to ignition of ignition composition 14, and is disposed in operative communication with ignition composition 14 to so detonate; and ignition composition 14 is ignitable in response to heat developed by passage of electric currentthrough lead wires 18 and bridge wire 22 to thereby initiate detonation of primer charge 13 and, in turn, base charge 11 In some embodiments a conventional delay fuse (not shown) is disposed between ignition mixture 14 and primer charge 13 to delay detonation after ignition. Also in some embodiments, other materials, eg diazodinitrophenol, can serve as a combined ignitioncharge 14 and primer charge 13, but in all events, base charge 11 is in operative communication with at least one other live' component in shell 9, for effecting its detonation.

End section 12' of shell 9 contains base charge 11 extending from shell end 12 upwardly into shell 9 Shell end closure 12 contains a passageway 24 communicating base charge 11 with the outside of shell 9. Passageway 24, when primary initiator 10 is under water, conveys water from outside shell 9 into base charge 11. The size of passageway 24 is correlated with at least one live component of shell 9, viz, at least one of charges 11, 13, and 14, so as to convey water in an amount to desensitize all or at least one of the components 11, 13, and 14, after a predetermined period of time following emplacement of the system in the watercovered shooting area. Generally it is desired to convey a sufiicient amount of water for infiltration of both base charge 11 and primer charge 13, particularly when primer 13 is diazodinitrophenol. It is an important req uisite of the invention that the size of passageway 24 is limited so as to preclude sufficient water flow to cause desensitization prior to expiration of the predetermined time period.

It is necessary, of course, that the complete explosive assembly remain operative for a predetermined or preset period to permit a suitable amount of time for emplacing the assembly in the Water-covered shooting area and shooting. This pre-set period is generally at least minutes and is often as long as from 30 minutes up to one hour, and sometimes longer, although the particular time period is not critical. The size of the opening 24 is dependent, therefore, on the predetermined time period selected, the particular primary initiator component or components to be desensitized, and bulk density and particle size of those components in the shell 9.

Some base charges 11 are more readily desensitized by water than are others. PETN, for example, is desensitized upon contact with water less readily than is RDX. However, a primer composition 13 is generally more easily desensitized than is a base charge 11, and it is accordingly general practice to correlate the size of passageway 24 to permit sufficient amount of water to have passed into, and infiltrated both charges 11 and primer 13 to effect the desensitization. In some such instances it is preferred to correlate size of passageway 24 to permit sufiicient water to pass into and through all three charges 11, 13, and 14.

Generally, the size of passageway 24 is selected, for such correlations, to have a substantially constant crosssectional area, equal to that of a circle having a diameter of from about to inch. For example, when 0.4 gram pressed PETN, 0.26 gram diazo and 0.10 gram ignition composition are utilized in the primary initiator system 10 and the predetermined minimum time period is 15 minutes, the cross-sectional diameter of a cylindrical passageway 24 is about 7 inch.

With reference to FIG. 2 is shown a cross-sectional View, of a lowermost end portion of the primary initiator of FIG. 1, containing a water-resistant member 23 in end section 12', having a cross-sectional area greater than that of passageway 24, at the inner wall of shell end 12, and shaped, and superposed on passageway 24', as a closure therefor. Water-resistant closure 23 serves sufficiently as a water barrier to protect the interior of shell 9 from ingress of desensitizing amounts of water during the entire operating period, i.e. the predetermined period of time allowed for normal operation, but becomes completely dissolved in the water in contacttherewith, or it allows passage of water because of its porosity to permit flow of water into the shell through passageway 24', to provide the required desensitization after the pre-set period. Passageway 24 is the same as passageway 24 of FIG. 1 except that it is generally larger.

This embodiment is most advantageously utilized when the primary initiator is to be under water for relatively long periods before shooting, for periods in the order of one hour or longer. Exemplary materials forming element 23 are paper and a water-soluble material such as Klucel (hydroxypropyl cellulose), CMC, poly(vinyl alcohol), and the like. The primary requisite of the element 23 is that it become completely dissolved or disintegrated in the water in contact therewith, or that it allow passage of water because of its porosity to permit the requisite flow of water from passageway 24' into the interior of shell 9 to accomplish desensitization of the particular component, or components, as described.

With reference to FIG. 3, is secondary initiator system 30 of the booster type, comprising elongated shell 31 containing booster charge 32, upwardly extending from bottom end 29 of shell 31, as a base charge of high explosive. Charge 32 can be the same as base charge 11 of FIGS. 1 and 2, except that in some instances it is advantageous that there be a minimum amount of free volume in the charge as described in more detail hereinafter. Cap well 33 for accepting a primary initiator system such as electric blasting cap assembly 10 of FIG, 1 extends coaxially into shell 31 through upper closed end 34 into booster charge 32 generally for a distance of from about A to V; the length of shell 31.

Bottom end 29 of shell 31 contains a passageway 28,

communicating charge 32 With the outside of shell 31.. When secondary initiator system 30 is under the water ur p ssa y 28 e e t snnve o of te from outside the shell 31 into charge 32 to effect desensitization of charge 32 after a predetermined, or pre-set, period of time. The size of passageway 28 is correlated with the charge 32 so as to deliver sufficient water for desensitization of charge 32 after the above pre-set period of time which allows for emplacement of the explosive assembly and completing the shot.

The correlation of the size of passage 28 with charge 32 to effect the requisite water flow through passage 28 is determined by the particular charge 32 and by the bulk density and particle size thereof. The amount of free volume in charge 32 is an important factor in determining the requisite correlation, desensitization being more readily accomplished when there is an appreciable amount of free volume. Bulk density of the charge 32 in shell 31 is, therefore, a factor to be considered. A suitable bulk density, for example, is obtained with reference to RDX, when a shell 31 having a volume (not including that of well 33) of about cc, contains from about 17- 20 grams RDX. When the charge 32 is PETN, a somewhat lower ratio of grams of charge to the volume of shell 31 can be utilized. It is important in all events that once the charge 32 has been selected, its bulk density in shell 31 be correlated with the size of passageway 28 to permit requisite flow of water for accomplishing the desensitization after the predetermined time period.

In one form of now-preferred practice, any suitable water-wetting agent can be utilized as an ingredient of charge 32 to shorten wetting time and also to permit a larger proportion of water to be absorbed per unit time for a greater desensitization efficiency. Exemplary wetting agents are any suitable surfactant such as Aerosol O.T.B (85 percent ester of a sulfonated carboxylic acid and 15 percent sodium benzoate), Petro-Ag (a sodium salt of a sulfonated naphthalene), and the like, generally in an amount of from 0.1 to about 2 weight percent. Similarly, an effervescing material, upon contact with water, such as sodium bicarbonate and sodium bitartrate, and the like, can be utilized as an ingredient of the charge 32 to regulate bulk density to increase free volume for increased desensitization efficiency.

In another form of preferred practice, an increase in free volume of the charge 32, which is a function of bulk density and particle size, is obtained, if a limited portion of the charge 32 is replaced with a water-soluble salt such as ammonium nitrate or sodium nitrate. In carrying out that practice, water, from passageway 28, infiltrating the charge 32 dissolve the water-soluble salt ingredients to provide voids for increased free volume within the charge 32 and accompanying increase in desensitization efficiency. A charge 32 containing up to 30 percent sodium nitrate and up to as high as 60 percent ammonium nitrate has been advantageously utilized.

In preferred practice the size of passageway 28 in shell 31, after correlation with charge 32, as above described, is such that its cross-sectional area is substantially constant and is equal to that of a circle having a diameter of from about to A inch, based on an 18 to 22 gram charge 32.

With reference to FIG. 4, is shown a cross-sectional view, in part, of a lowermost portion of the initiator of FIG. 3, which is the same as that of FIG. 3 except with reference to water-resistant member 36 in shell 31. Member 36 has a greater cross-sectional area than that of passageway 28, at the inner wall of shell end 29, and is shaped, superposed on passageway 28' as a closure therefor. Water resistant closure 36 serves sufliciently as a water barrier to protect the interior of shell 31 from ingress of desensitizing amounts of water during the preset operating period, but becomes completely dissolved in the water in contact therewith, or because of its porosity permits flow of water into shell 31 through passageway 28' to provide the required desensitization after the pre-set period, The embodiment of FIG. 4 protects charge 32 from undue ingress of water during the predeter mined, or pre-set, period for normal underwater operation but is most advantageous in that it provides for use of a passageway larger than that of passageway 28 of FIG. 3 to permit a higher rate of flow of water into shell 31 to more quickly effect desensitization of the entire volume of charge.

Member 36 can be any suitable water-permeable or water-soluble material such as that described herein above with reference to element 23 of FIG. 2. The primary requisite of the element 36 is that after the pre-set period, it becomes completely dissolved in the water in contact therewith or that it allow passage of water because of its porosity to permit the requisite flow of water from passageway 28 into the interior of shell 31 to accomplish desensitization of the base charge, as described.

The use of a water-resistant member 36 is particularly advantageous when utilizing a hygroscopic water-soluble salt as an ingredient of the charge 32, inasmuch as it precludes premature water solution of the water-soluble salt during the pre-set operating period.

When utilizing a closure member 36 in the secondary initiator system of FIG. 4, the size of the passageway 28 is generally larger than that of the passageway 28 of FIG. 3. Thus, by way of example, the cross-sectional area of passageway 28' can advantageously be that of a circle having a diameter of from A; to inch, when utilizing a charge 32 of, say, 20 grams.

The embodiment of FIG. 4 is the now-preferred secondary initiator system of the invention, and particularly when the base charge 32 is RDX with ammonium nitrate, say, in the order of from about /10 to 70/30 RDX/ AN, and 80/20 being particularly preferred.

With reference to FIG. 5 is shown a complete explosive assembly containing the primary and secondary initiator systems of the invention, and connecting with long communication lines utilized in offshore seismic operations. The complete explosive assembly 38 comprises elongated cartridge shell 39 containing booster well 41 extending coaxially into shell 39 through top end 42 and adapted to accept a secondary initator assembly of the invention. Now-preferred secondary initiator 30' (FIG. 4) of the invention is supported in booster well 41 and a now-preferred primary initiator system 10 in FIG. 1 is supported in cap well 33 of initiator 30'. Shell 39 contains main charge 40 which substantially fills shell 39 and in all events is in detonating relationship with the secondary initiator system 30 in well 41.

Also shown are lead lines 13 from initiator 10, connecting with shot firing cable 43 leading to the energy, or power, source, in many instances, up to yards or more distant.

When a misfiring occurs, and assembly 38 is lost, the assembly sinks to the bottom of the water area and after some time is, due to the various water movements, washed from one point to another, and in many instances ultimately it reaches the shoreline. In the process of being washed about, the still live initiators are often dislodged from the assembly, but in all events either the assembly, intact, or one or more of the dislodged live components thereof, reach the shorelines with the accompanying safety hazards.

During the normal operating time, water finds its way into the cap well 33 (FIG. 5) of the secondary initiator 30, i.e. between the inner wall of the well 33 and the primary initiator 10 therein. As provided by the invention, water gains access through passageway 24 into primary initiator 10 and desensitization of the primary initiator 10 takes place as described with reference to FIG. 1. Whether subsequent to a misfire there is separation of the complete explosive assembly 38 into its components, or whether the said assembly remains intact is immaterial. In either event live initator components reaching the shore have previously become desensitized as described above.

The invention is illustrated with references to the following examples.

7 Example I A series of primary initiators of FIG. 1 was made up as follows:

Each initiator was an instantaneous electric blasting cap formed from an aluminum shell, 1.97" long and having an inside diameter of 0.256 along the shell section containing the base charge primer and ignition composition, except for a paper sleeve described hereinafter. The base charge was 0.4 gram PETN-graphite (98/2) pressed flat to 0.36. The primer charge was 0.26 gram of loose diazodinitrophenol. The ignition charge was 0.09 gram of a lead mononitroresorcinate (LMNR)/potassium chlorate/nitrostarch, milled mixture buttered in a paper sleeve, 0.250" long, 0.205 ID. to form a cavity of 9.200" diameter by 0.125 for containing the buttered ignition charge. The paper sleeve, the ignition composition, primer and base charge Were supported in place by a series of closure plugs, viz aluminum/candelilla Wax/marasperse, Bakelite, and cast resin, also serving as closure plugs. The lead wires were No. 20 copper wire, and the bridge wire was a gold-plated Tophet C wire having a resistance of 445 ohms per yard.

The shell contained a passageway through the bottom thereof of inch diameter, thus directly cmmunieating the base charge with points outside the shell.

In carrying this series of tests, as shown with reference to the following tabulation, a number of the electric blasting cap initiators thus prepared were placed under salt water at hydrostatic heads of and 50 feet for varying lengths of time and then tested for sensitivity, utilizing the standard 1" X 1" x Vs thick lead plate test, As shown in the tabulation, at a hydrostatic head of 10 feet, there were some D shots after hours and even after 40 hours. In this particular system there were still some A shots. However, under the higher hydrostatic head there were 25 D shots for the 25 caps tested after 17 hours and, of course, also after 40 hours. The tests demonstrate substantially complete desensitization of primary initiators accomplished in practice of the invention.

Exposure to 10 ft. of 312% Salt Water Time (hrs) Number Tested Results 0.25 20A 0.5 20 20A 2.0 20 20A.

Exposure to 50 ft. of 39%% Salt Water (Simulated) 4 20 2A, B, 17D 17 25 25D 40 25 25D A= Good Shot-Hole in plate.

B =Poor Shot-No Hole in plate (back of plate ruptured).

C=P0or Shot-No hole in plate (back of plate bulged, but not ruptured).

D=Poor ShotNo bulge, no rupture.

*only A plates will detonate booster.

Example 2 In another; series of tests a number of secondary initiators of FIG. 4 containing 22 grams RDX/ aerosol (a wetting agent described above), 98/2, was placed in a shell of about 17 cc. volume, excluding the volume of the well, containing a passageway of A" diameter in the bottom end. Fifty (50) such initiators were tested and shot in accordance with a witness plate method utilizing a /8" x 6 x 6 cold-rolled steel sheet, utilizing a No. 8 commercial blasting cap initiator, as a measure of desensitization after prolonged periods under water at 25 p.s.i.g. After 2.1 weeks desensitization was complete, as indicated by failure of any of the units tested, to break a hole in the steel witness plate, due to failure of the booster to detonate.

In carrying out this test all 50 units were placed under water at the same time and were tested in multiples of 10 over the 2.1-week period.

The above tests were repeated except that the initiator contained 20 grams of base charge, i.e. instead of 22 grams. All shots failed the plate test after 1.2 weeks.

In another repetition of the above tests, except that 21- grams of base charge was utilized, there was present also 20 percent of ammonium nitrate. One hundred percent failure of the plate test was observed after 0.52. week.

Example 3 Four hundred and seventy-five (475) initiator units of FIG. 1 were taken from plant production lots and held under 3.5 percent salt water solution for 20 hours at 25 p.s.i.g. Four hundred and seventy-one (471) of these gave D plates in accordance with the plate-test method of Example 1, with 3 C plates and l B plate. This example demonstrates the desensitization accomplished in the practice of the invention, inasmuch as no A plates were obtained.

Example 4 It is desirable from a practical point of view that the preset period for norm-a1 operation be in the order of 15 minutes, i.e. in order to allow for emplacement of the explosive charge and firing. Accordingly, 15 initiators of Example 1 were held under 10 feet of 3.5 percent salt solution Water for 15 minutes to determine whether desensitization was too rapid. Fifteen (15 A plates were obtained thus demonstrating the integrity of these units within the preset time period.

Example 5 Ten (10) of the initiator units of Example 1, except that each contained a 91 inch passageway through the bottom thereof, were placed under 10 feet of 3.5 percent salt water solution and held for /2 hour. There were 10 D plates obtained, showing desensitization after that period of time.

An additional ten of those initiator units were tested except that the passageway was covered with a layer of lacquer at the inner wall of the shell. In this case there were four D shots and 6 A shots indicating the retarding of water flow due to the coverage of the passageway with a water-soluble lacquer.

The same tests were repeated except that in place of the lacquer covering, 100 mg. of pressed CMC (carboxymethylcellulose) was placed over the passageway in place of the water-soluble lacquer. Nine (9') A shots were obtained along with 1 D shot, again indicating the role of the water-soluble cover over the passageway to regulate the ingress of water for desensitization.

When referring herein to desensitization it is meant that the component is so desensitized as to fail to perform its intended function.

As will be evident to those skilled in the art, various modifications can be made or followed, in the light of the foregoing disclosure and discussion, without departing from the spirit or scope of the disclosure or from the scope of the claims.

What we claim and desire to protect by Letters Patent 1. An initiator system of the blasting cap and booster type, for initiating explosives in water-covered areas, which comprises an elongated closed shell, and a base explosive charge within said shell, as at least one live initiator component of said system, extending from the shell closure at one end of said shell toward the opposite end thereof; said shell containing a passageway in the said closure end adjacent said base charge to communicate said base charge with the outside of said shell; the size of said passageway being correlated with at least one live component within said shell to convey flow of water from outside said shell to the shell interior to cause desensitization of the last said component after a predetermined period of time following emplacement of said system in said water-covered area; and when said initiator system is of the blasting cap type, said passageway being open and unobstructed so as to directly communicate the interior of said shell with the outside thereof.

2. A primary initiator system of the blasting cap type for use in water-covered areas, comprising an elongated closed shell, and a base explosive charge within a bottom end section of said shell; a primer charge superposed on said base charge, within said shell; an ignition composition superposed on said primer charge, within said shell; means, within said shell, for ignition of said ignition composition; a passageway, in the bottom closure end of said shell, unobstructed so as to directly communicate said base charge with the outside of said shell; and the size of said passageway being correlated with at least the said primer charge to convey flow of water from outside said shell to the shell interior to cause desensitization of said primer charge after a predetermined period of time following emplacement of said system within said water-covered area.

3. A primary initiator system of the blasting cap type for use in a water-covered area, comprising an elongated closed shell, and a base explosive charge within a bottom end section of said shell; diazodinitrophenol superposed on said base charge, within said shell, as a combined primer-ignition composition; means within said shell for ignition of said diazodinitrophenol; a passageway, in the bottom closure end of said shell, unobstructed so as to directly communicate said base charge with the outside of said shell; and the size of said passageway being correlated with said diazodinitrophenol to convey flow of water from outside said shell to the shell interior to cause desensitization of said diazodinitrophenol after a predetermined period of time following emplacement of said system within said water-covered area.

4. In a primary initiator system of claim 2, a pair of electrical conductor wires extending into said shell through the top closure end thereof and terminating in contact with said ignition composition, and a resistancewire connecting the terminal ends of said conductor wires in said shell; and said passageway having a substantially constant cross-sectional area equal to that of a circle having a diameter of from to inch.

5. A secondary initiator system of the booster type, comprising an elongated closed shell, and a base explosive within a bottom end section of said shell; a well member extending into said shell through a top end thereof for accepting a primary initiator; -a passageway in the bottom end closure of said shell to communicate said base charge with the outside of said shell, and the size of said passageway being correlated with said base charge to convey flow from outside said shell to the shell interior to cause desensitization of said base charge after a predetermined period of time following emplacement of said system below the water surface in said watercovered area.

6. In an initiator system of claim 5, a water-resistant member Within said shell, superposed on the end of said passageway adjacent the interior of said shell as a clossure therefor, and adapted to yield to flow of Water into said shell through said passageway to effect said desensitization after said predetermined period of time, whereby the size of said passageway can be correspondingly larger for quicker desensitization of said base charge.

7. A secondary initiator system of claim 5 wherein said passageway is substantially of constant cross-sectional area equal to that of a circle having a diameter of from /8 to A inch.

8. A secondary initiator system of claim 6 wherein said passageway has a substantially constant cross-sectional area equal to that of a circle having a dimeter of from A to a inch.

9. A secondry initiator of claim 6 wherein said base charge comprises RDX and up to parts by Weight of ammonium nitrate per parts of total base charge.

10. A secondary initiator of claim 6 wherein said base charge contains up to 2 weight percent of a Water-wetting agent.

References Cited UNITED STATES PATENTS 2,709,407 5/1955 Lowe 102-24 2,739,535 3/1956 Rolland et al. 102-28 2,759,417 8/1956 ONeill 10228 X 2,966,822 1/ 1961 Kistiakowsky et al. 86-1 3,123,507 3/1964 Butts et al. 14992 X 3,132,585 5/1964 Higashishima et al. 10228 3,279,372 10/1966 Patterson 10228 BENJAMIN A. BORCHELT, Prim'ary Examiner. VERLIN R. 'PENDEGRASS, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,358,601 December 19, 1967 David J. Dittmann et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 48, for "dissolve" read dissolves column 7, in the tabulation, in the first main heading, for "3-l2%" read 3 1/2% in the same tabulation, in the second main heading, for "39 l/2%" read 3 1/2% Signed and sealed this 11th day of February 1969.

SEAL) LttCSt;

dward M. Fletcher, Jr. EDWARD J. BRENNER rttesting Officer Commissioner of Patents 

1. AN INITIATOR SYSTEM OF THE BLASTING CAP AND BOOSTER TYPE, FOR INITIATING EXPLOSIVES IN WATER-COVERED AREAS, WHICH COMPRISES AN ELONGATED CLOSED SHELL, AND A BASE EXPLOSIVE CHARGE WITHIN SAID SHELL, AS AT LEAST ONE LIVE INTITIATOR COMPONENT OF SAID SYSTEM, EXTENDING FROM THE SHELL CLOSURE AT ONE END OF SAID SHELL TOWARD THE OPPOSITE END THEREOF; SAID SHELL CONTAINING A PASSAGEWAY IN THE SAID CLOSURE ENE ADJACENT SAID BASE CHARGE TO COMMUNICATE SAID BASE CHARGE WITH THE OUTSIDE OF SAID SHELL; THE SIZE OF SAID PASSAGEWAY BEING CORRELATED WITH AT LEAST ONE LIVE COMPONENT WITHIN SAID SHELL TO CONVEY FLOW OF WATER FROM OUTSIDE SAID SHELL TO THE SHELL INTERIOR TO CAUSE DESENSITIZATION OF THE LAST SAID COMPONENT AFTER A PRE- 